1. Field of the Invention
The present invention relates to a system and method for electron beam irradiation that is used, for example, to make recordings on an optical master disk.
2. Description of Related Art
In recent years, the optical disk manufacturing industry has faced demands for higher recording densities. To achieve this, it is necessary to form smaller recording pits. Therefore, a machine for shining an electron beam at a master disk to make recordings has been proposed for manufacturing of optical master disks, it being noted that the electron beam is capable of forming smaller pits than are done by the prior art laser light. This proposed machine needs to accurately focus the electron beam in a corresponding manner to the master disk to permit accurate recordings.
One known electron beam irradiation system fitted with this means for focusing the electron beam is shown in FIG. 6, where an inverting table 41 that can be rotated by an inverting mechanism 42 is mounted inside a vacuum vessel 40. An electric motor 43 is fixedly mounted on the side of one end of the inverting table 41. A turntable 44 is mounted to the rotating shaft of the motor 43, and a master disk 45 is placed on the turntable 44. An electron beam is shone at the master disk 45 from electron beam irradiation portion 46 to make recordings.
In this known system, a focusing stage 47 is mounted at the other end of the inverting table 41, i.e., on the opposite side of the center of rotation of the table 41 from the turntable 44, to bring the electron beam into focus. The top surface of the focusing stage 47 is set flush with the master disk 45 placed on the turntable 44. To make recordings on the master disk 45, the focusing stage 47 is first made to correspond to the electron beam irradiation portion 46. Under this condition, the electron beam is shot at the top surface of the focusing stage 47, and the beam is focused with the electron beam irradiation portion 46. Then, the inverting table 41 is rotated through 180xc2x0 (i.e., inverted) by the inverting mechanism 42 to make the master disk 45 correspond to the electron beam irradiation portion 46. In this state, the electron beam is shot at the master disk 45 to make recordings.
The prior art electron beam irradiation system constructed in this way has the following problem. This system is so designed that the master disk and the focusing stage are inverted and moved. Therefore, the master disk and focusing stage are spaced apart widely. Consequently, it is difficult to maintain them flush with each other accurately. Hence, it is difficult for this prior art system to align the focus of the electron beam to the master disk accurately. It is doubtful that accurate recordings will be accomplished.
Furthermore, in a machine utilizing an electron beam, the beam irradiation conditions are liable to change during the operation. Therefore, the probe current and the diameter of the beam can preferably be quantitatively measured in order to monitor the performance of the machine and to maintain and service it.
It is an object of the present invention to provide a system satisfying this requirement.
This object is achieved by an electron beam irradiation system having (a) a support mechanism portion having a slide table for holding a target irradiated with an electron beam such that the target can move radially, (b) electron beam irradiation portion for shooting the electron beam while keeping a part of the space lying over the target in a vacuum, and (c) a focusing stage for bringing the electron beam into focus. The focusing stage is fixedly mounted in a position adjacent to the target on the slide table of the support mechanism portion. This system is characterized in that the electron beam irradiation portion has a focusing lens for sharply focusing the electron beam onto the target and a deflector for scanning the beam in two dimensions. The system is also characterized in that the focusing stage has a built-in Faraday cup having a knife edge, the cup being capable of detecting the incident current.
The present invention also provides an electron beam irradiation method using an electron beam irradiation system having (a) a support mechanism portion having a slide table for holding a target irradiated with an electron beam such that the target can move radially, (b) electron beam irradiation portion for keeping a part of the space lying over the target in a vacuum and shooting the beam, the electron beam irradiation portion (b) being fitted with a focusing lens for sharply focusing the beam onto the target, the electron beam irradiation portion (b) being also fitted with a deflector for scanning the beam in two dimensions, and a focusing stage (c) for bringing the electron beam into focus. The focusing stage (c) has a built-in Faraday cup fixedly mounted in a position adjacent to the target on the slide table of the support mechanism. The Faraday cup has a knife edge and is capable of detecting the incident current as the beam is scanned across the knife edge. This method comprises the steps of: varying the focus of the beam using the focusing lens; scanning the beam across the knife edge using the deflector; detecting the output signal from the Faraday cup to thereby measure the diameter of the beam; optimizing the conditions of the focusing lens based on the results of the measurement to thereby focus the beam; and then moving the slide table and shooting the beam at the target.
Furthermore, the present invention provides a method of shooting an electron beam by the use of an electron beam irradiation system having (a) a support mechanism portion having a slide table for holding a target irradiated with an electron beam such that the target can move radially, (b) electron beam irradiation portion for keeping a part of the space lying over the target in a vacuum and shooting the beam, the electron beam irradiation portion (b) having a focusing lens for sharply focusing the beam onto the target, a deflector for scanning the beam in two dimensions, and a detector for detecting electrons emitted from a surface of the target by electron beam irradiation, and (c) a focusing stage for focusing the beam. The focusing stage is fitted with a Faraday cup fixedly placed in a position adjacent to the target on the slide table of the support mechanism portion. The Faraday cup has a built-in knife edge and is capable of detecting the incident current as the beam is scanned across the knife edge. This method comprises the steps of: shooting the beam onto the focusing stage while scanning the beam in two dimensions using the deflector; obtaining an SEM image by detecting electrons produced from the irradiated surface using the detector; setting the conditions of the focusing lens such that the sharpest SEM image is obtained while varying the focus of the beam using the focusing lens to thereby focus the beam; scanning the beam across the knife edge using the deflector; detecting the output signal from the Faraday cup to thereby measure the diameter of the beam; and then moving the slide table and shooting the beam at the target.
In the electron beam irradiation system described above, the electron beam is shot onto the focusing stage and the beam is brought to focus before recordings are made on the master disk. Then, the slide table is moved to a position where the master disk is started to be irradiated with the beam. The beam is shot onto the master disk, thus making recordings on it.
In this electron beam irradiation system according to the present invention, the distance between the master disk and the focusing stage is short. This is advantageous in increasing the accuracy at which the focusing stage is aligned to the master disk. Consequently, the electron beam can be focused accurately. This enables accurate recordings.
Other objects and features of the invention will appear in the course of the description thereof, which follows.